As is well known, dye complexes, especially azo dye complexes, both the metallized kind and the non-metallized kind, are not environmentally friendly, although they are commercially important in the dyeing of textiles because the dyed textiles, particularly those dyed with metallized azo dye complexes, show excellent lightfastness, rubbingfastness, and washfastness.
In other words, there is a problem of water pollution from the azo dye complexes, not only from contaminants in the form of BOD (biological oxygen demand) and COD (chemical oxygen demand), but also from contaminants in the form of color bodies, that are discharged into public water supplies. An excellent background discussion of azo dye complexes, both the metallized kind and the non-metallized kind, can be seen in Beffa and Back, "Metal-Complex Dyes for Wool and Nylon--1930 to Date", Vol. 14, Rev. Prog. Coloration, pp. 33-42 (1984), and in U.S. Pat. No. 5,376,151 to Freeman et al. It is noted that metallized azo dye complexes typically employ metal ions such as chromium ion, copper ion, iron ion, cadmium ion, and cobalt ion.
Related to the problem that azo dye complexes create colored effluent is the problem that paper mills also create colored effluent. Of interest in connection with removal of color from paper mill wastewaters are U.S. Pat. No. 3,578,587 to Kemmer and U.S. Pat. No. 4,089,780 to Svarz et al. More specifically, the patent to Kemmer shows a process for using a substantially lesser amount of lime (CaCO.sub.3), together with an anionic water-soluble polymer having a molecular weight of at least 100,000 for treating effluent from paper mills in order to remove color as a precipitate. Also, the patent to Svarz et al. shows a process for using a water-soluble polyamine, followed by a water-soluble anionic or non-ionic organic polymer having a molecular weight of at least 10,000 for treating paper mill effluent to remove color as a precipitate.
Additionally, of interest in connection with polymeric treatment of effluent is U.S. Pat. No. 5,178,774 to payne et al. Disclosed is a process for separating coagulatable material from an aqueous suspension by employing an ionic polymer in the form of dry solid particles.
Of note, treatment of effluent with potassium permanganate is shown in U.S. Pat. No. 1,088,063 to Drechsler and U.S. Pat. No. 3,483,120 to Hatch. It is interesting that U.S. Pat. No. 3,483,120 to Hatch specifically teaches, at lines 69-72 of column 2, that "certain anionic polymers are shown to be relatively inefficient, as compared to cationic polymers, when employed conjunctively with the permanganate."
Furthermore, treatment of effluent with hydrogen peroxide as an oxidizing agent is shown in U.S. Pat. No. 3,361,528 to Shen; U.S. Pat. No. 3,721,624 to Fisch et al.; and U.S. Pat. No. 4,804,480 to Jayawant.
Finally, of interest with respect to treatment of effluent is U.S. Pat. No. 4,800,039 to Hassick et al. Disclosed is a composition for reducing turbidity in aqueous systems, the composition being a combination of aluminum chlorohydrate, together with either one or both of certain kinds of polyamines or certain kinds of dialkyl diallyl ammonium polymers.
The disclosures of all of the above-mentioned patents are incorporated herein by reference.